function calc(a,b,callback){
    return callback(a,b)
}
function calc(a,b,callback){
    return a+b
}
function calc(a,b,callback){
    return a*b
}
let a=calc(10,20,plus)
let b=calc(10,20,(a,b)=>(a/b))
console.log(a,b);
dan=[1,2,3,4];

console.log(dan.length);
